1. Field of the Invention
The present invention mainly relates to a relay server that enables communication between devices connected to different LANs (Local Area Networks).
2. Description of the Related Art
Conventionally, there is a well known communication technology called a Virtual Private Network (VPN) in which LANs located in physically distant positions conduct communication with each other. In an example illustrated in a well-known document, for example, a relay server, a communication terminal, and the like are connected to each of a plurality of LANs installed at locations that are physically distant from each other. Using the VPN, the communication terminal can transmit a packet to the communication terminal connected to another LAN. Specifically, the packet is first transmitted from the communication terminal to the relay server in the same LAN. The relay server transmits via the Internet the packet to the relay server in the same LAN as the destination communication terminal. The relay server that receives the packet then transmits the packet to the destination communication terminal.
By using the VPN, another remotely-located LAN can be used as if the remotely-located LAN is a directly-connected network.
In this type of system, terminals conduct communication with each other using IP addresses (private IP addresses) of the terminals connected to the LAN. Accordingly, in the case where the communication is conducted using the VPN, it is necessary to transmit the IP address set to initiating LAN to the LAN of the other side.
From this viewpoint, for example, in the case where the VPN is constructed in the same company, a problem hardly occurs even if the other side learns the IP address. However, in the case where the VPN is constructed in different companies, from the viewpoint of security, it is undesirable that the other side learns the IP address. Accordingly, there is a need for a configuration in which the VPN can be operated such that the IP address provided to a device in the LAN cannot be learned by the other LAN side.